Cellular telephone operable on different cellular telephone systems

ABSTRACT

A unique dual-system cellular telephone includes a transceiver (100) having a dual bandwidth receiver, an audio/logic unit (200) having dual control programs, and a handset unit (300). The dual bandwidth receiver of the transceiver (100) has different filters (408 and 410) in the intermediate frequency section thereof which are switchably selected depending on which cellular telephone system is available. When service is not available in one of the cellular telephone systems, the unique cellular telephone automatically switches the receiver bandwidth and control program for operating on the other cellular telephone system.

This is a continuation of application Ser. No. 370,675, filed June 23,1989 and now abandoned.

BACKGROUND OF THE INVENTION

The present invention is generally related to radiotelephones, and moreparticularly to an improved cellular telephone for operating on twodifferent cellular telephone systems.

Cellular telephones currently are designed to operate on only one typeof cellular telephone system. Most countries of the world have adoptedonly one type of cellular telephone system. Thus, cellular telephoneswhich operate on only one type of cellular telephone system have beenadequate for the cellular systems in most countries of the world. Insome countries, cellular systems have replaced and/or supplemented oldernon-cellular radio telephone systems. For instance, in the UnitedStates, cellular systems have replaced and/or supplemented thenon-cellular, improved mobile telephone systems (IMTS) which providedradio telephone services since the late 1960s. In order to allow use ofboth the IMTS systems and the cellular systems, a prior art radiotelephone included both an IMTS transceiver and a cellular transceiverwhich were coupled to a common handset control unit. In this prior artradio telephone, audio signals were switched by user selection fromeither the IMTS transceiver or the cellular transceiver to the commonhandset control unit. Use of two transceivers to provide services on twodifferent radio telephone systems is both bulky and relativelyexpensive. Another type of signal switching found in prior art testequipment is mechanical bandwidth switching of the intermediatefrequency (IF) section of the radio receiver in a modulation analyzer.The IF section of such test equipment was switched between two differentbandwidths by diode switching circuitry in response to user activationof a mechanical switch. However, mechanical IF bandwidth switching ofsuch test equipment is not suitable for use in cellular telephones andalso requires user intervention and additional circuitry, increasing thecost and complexity thereof. For the foregoing reasons, there is a needfor a cellular telephone which accommodates different receiverbandwidths for operating on different cellular telephone systems.

OBJECTS OF THE INVENTION

Accordingly, it is an object of the present invention to provide aunique dual-system cellular telephone which includes bandwidth switchingin the receiver thereof for automatically operating on differentcellular telephone systems.

It is another object of the present invention to provide a uniquedual-system cellular telephone which includes bandwidth switching in theintermediate frequency section of the receiver thereof and softwareswitching in the control unit for automatically operating on differentcellular telephone systems.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of the transceiver of a cellular telephoneembodying the present invention.

FIG. 2 is a block diagram of the audio/logic unit of a cellulartelephone embodying the present invention.

FIG. 3 is a block diagram of the handset unit of a cellular telephoneembodying the present invention.

FIG. 4 is a circuit diagram of the switched IF circuitry of the cellulartransceiver in FIG. 1.

FIG. 5 is a flow diagram for the process used by microcomputer 202 inFIG. 2 for signalling and communications in cellular system A.

FIG. 6 is a flow diagram for the process used by microcomputer 202 inFIG. 2 for signalling and communications in cellular system B.

FIG. 7 is a flow diagram for the process used by microcomputer 202 inFIG. 2 for processing interrupts and switching between cellular systemsA and B.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIGS. 1, 2 and 3, there is illustrated a block diagram ofthe transceiver 100, audio/logic control unit 200, and handset unit 300,respectively, of a dual-system cellular telephone embodying the presentinvention. Cellular telephone of the present invention may beadvantageously utilized in any country or cellular service area wheretwo different cellular telephone systems exist. For example, a TACS-typecellular telephone system and a US-type cellular telephone system mayprovide at least partial overlapping cellular telephone service to thesame geographical area. Currently, both Japan and Hong Kong haveapproved two different cellular telephone systems. In cities or highwayswhere only one of the two cellular telephone systems provides cellularservice, the cellular telephone of the present invention automaticallyswitches to the serving cellular system insuring that the user willalways have access to available cellular service. For convenience, twodifferent exemplary cellular telephone systems will be referred to ascellular system A and cellular system B hereinbelow.

Referring next to the block diagram in FIG. 1, transceiver 100 ispreferably a cellular transceiver operable in the transmitter frequencyrange from 915 to 940 MHz and the receiver frequency range from 860 to885 MHz. Except for block 150, the blocks of transceiver 100 may beimplemented by conventional cellular transceiver circuitry, such as, forexample, the circuitry of the US-type cellular telephone transceivershown and described in Motorola Instruction Manual No. 68P81070E40,entitled "DYNATAC Cellular Mobile Telephone," published by and availablefrom Motorola C & E Parts, 1313 East Algonquin Road, Schaumburg, Ill.60196.

RF signals on cellular radio channels are transmitted and received bytransceiver 100 via antenna 120 and harmonic filter 122. RF signals fortransmission by antenna 120 are applied to harmonic filter 122 bytransmitter duplex filter 126 via duplex transmission line 124. Thetransmitting circuitry of transceiver 100 includes offsetvoltage-controlled oscillator (VCO) 108, offset mixer 110, poweramplifier 112, and directional coupler 114, which generate thetransmitter signal of the RF channel to which transceiver 100 is tuned.Synthesizer 104 is coupled to reference oscillator 102 for generatingthe receiver injection signal which is split by splitter 106 and coupledto offset mixer 110 and injection filter 116. Synthesizer 104 is tunedto a particular radio channel by audio logic control unit 200 using datasignal 907, clock signal 906, and RX enable signal 905. Offset VCO 108is coupled to reference oscillator 102 for generating an offset signalwhich is mixed with the receiver injection signal in offset mixer 110 togenerate the transmitter signal. The circuitry of offset VCO 108 ispowered up and down in response to the TX prekey signal in order to savestandby current drain. Amplifier 112 is responsive to PA control signal902 from audio/logic control unit 200 for generating up to eightdifferent power levels at its output. Directional coupler 114 producesRF detect signal 901 which has a magnitude that is proportional to themagnitude of the output of amplifier 112. RF detect signal 901 fromdirectional coupler 114 is coupled to audio logic control unit 200,where it is converted to digital form and used to generate PA controlsignal 902 for maintaining the output of amplifier 112 at the desiredpower level.

In the receive path of transceiver 100, receive signals are coupled fromharmonic filter 122 by duplex transmission line 128 to receiver duplexfilter 130, RF amplifier 132, receiver filter 134 and transmission line136 to first mixer 138, where the filtered RF signals are mixed with thereceiver injection signal from injection filter 116 and transmissionline 118 to produce the first IF signal. The first IF signal from firstmixer 138 is coupled to crystal filter 140, IF amplifier 142 and crystalfilter 144 for selecting the desired component thereof. The output ofcrystal filter 144 is coupled to second mixer 148, where it is mixedwith second local oscillator 146 to produce the second IF signal. Thesecond IF signal from second mixer 148 is coupled to switched IF filter150, which includes first and second filters having different bandwidthsfor selecting the desired components thereof for cellular system A andcellular system B, respectively.

In the preferred embodiment, the first filter in switched IF filter 150has a wide bandwidth, that is a 3 dB bandwidth of ±12 KHz, and thesecond filter in switched IF filter 150 has a narrow bandwidth, that isa 3 dB bandwidth of ±6 kHz. In practicing the present invention,switched IF filter 150 may include additional filters for selecting thedesired components thereof for additional cellular systems over andabove cellular systems A and B. Bandwidth control signal 908 fromaudio/logic control unit 200 is coupled to switched IF filter 150 forswitching between the first and second filters thereof. When bandwidthcontrol signal 908 has a binary one state, the first filter of switchedIF filter 150 is selected for providing a wide bandwidth for cellularsystem A. When bandwidth control signal 908 has a binary zero state, thesecond filter of switched IF filter 150 is selected for providing anarrow bandwidth for cellular system B. The output of switched IF filter150 is coupled to detector 152 which produces discriminator audio signal909 and received signal strength indicator signal (RSSI) 910, whichsignals are coupled to audio/logic control unit 200.

Referring next to the block diagram of FIG. 2, audio/logic control unit200 includes microcomputer 202 which controls the operation oftransceiver 100 in accordance with a control program stored EPROM memory204 and including a first portion for signalling and call processing incellular system A, a second portion for signalling and call processingin cellular system B, and a third portion for the user interface incellular systems A and B. In the preferred embodiment, microcomputer 202is a Motorola type 68HC11 microprocessor integrated circuit.Microcomputer 202 is also coupled to EEPROM memory 206 for accessingtelephone numbers, serial numbers, and other call processing informationstored therein. In the preferred embodiment, the dual-system cellulartelephone of the present invention has two telephone numbers, one forcellular system A and another for cellular system B. Microcomputer 202is coupled to audio circuitry 210 for controlling transmit and receiveaudio paths, the microphone signal 911 and the RX HI signal,respectively, for operation in both cellular systems A and B. Audiocircuitry 210 is described in further detail in U.S. Pat. No. 4,741,018.For operation in cellular system A, microcomputer 202 is coupled tosignalling circuitry 208 for generating and processing high-speedsignalling data (FWD DATA and REV DATA), supervisory audio tones (FWDSAT and REV SAT), and dual tone multifrequency dialing signals (LOW DTMFand HIGH DTMF) utilized in call processing. Signalling circuitry 208 isdescribed in further detail in U.S. Pat. Nos. 4,302,845 and 4,312,074.When operating in cellular system B, low-speed signalling data indiscriminator audio signal 909 from transceiver 100 is coupled tomicrocomputer 202 by way of receiver filter 212 and limiter 214.Low-speed signalling data from microcomputer 202 for transmission incellular system B is coupled by transmitter filter 216 to modulationsignal 904 for application to offset VCO 108 of transceiver 100. DCcontrol circuitry 218 is responsive to ON/OFF signal 916 from handsetunit 300 and ignition sense signal 917 from the vehicle ignition switchfor generating the reset signal for initializing microcomputer 202,signalling circuitry 208 and audio circuitry 210, and generating the 5 Vand switched 9.5 V power supplies for powering the circuitry oftransceiver 100, audio/logic control unit 200 and handset unit 300. DCcontrol circuitry 218 includes conventional voltage regulators and isdescribed in further detail in U.S. Pat. No. 4,798,975.

Referring next to the block diagram of FIG. 3, handset unit 300 includesmicrocomputer 302 for scanning keypad 306 to detect activated keys andfor loading information into display 304 indicating telephone numbersand predetermined status of the dual-mode cellular telephone of thepresent invention. Handset unit 300 also includes microphone 310 andspeaker 314 which are coupled by amplifiers 308 and 312 to microphonesignal 911 and RX HI signal 912, respectively, and which may be switchedon and off by microcomputer 302. Handset unit 300 also includes severalindicators, one of which is a no-service indicator providing a visualindication of the availability of cellular service. Microcomputer 302generates the ON/OFF signal 916 in response to activation of the ON/OFFkey of keypad 306. Microcomputer 302 communicates with microcomputer 202of audio/logic control unit 200 via a three-wire data bus 913, 914 and915 which is illustrated and described in the U.S. Pat. No. 4,369,516.The TRU, CMP and RTN signals 913, 914 and 915 of the three-wire data busare buffered by amplifiers 316, 317 and 318, respectively. Handset unit300 may be located in a separate housing in the case of a mobilecellular telephone and may be located together with transceiver 100 andaudio/logic control unit 200 in a common housing in a case of portablecellular telephone.

Referring next to the circuit diagram of FIG. 4, there is illustratedthe detailed circuitry comprising the preferred embodiment of switchedIF filter 150 in FIG. 1. Switched IF filter 150 includes first filter408 and second filter 410 which are selected by bandwidth select signal908. The output of second mixer 148 is coupled to buffer amplifier 402,the output of which is applied to the input of analog switch 404. In thepreferred embodiment, analog switch 404 is a Motorola type MC14551 CMOSanalog switch integrated circuit. Analog switch 404 includes first andsecond switches 405 and 406 for coupling either first filter 408 orsecond filter 410 to detector 152. When the bandwidth select signal 908has a binary one state, first filter 408 is coupled by analog switch 404to detector 152. When bandwidth select signal 908 has a binary zerostate, second filter 410 is coupled by analog switch 404 to detector152. In the preferred embodiment, first filter 408 is a 455 kHz ceramicfilter having a wide bandwidth, that is a 3 dB bandwidth of ±12 kHz, andsecond filter 410 is a 455 kHz ceramic filter having a narrow bandwidth,that is a 3 dB bandwidth of ±6 kHz.

Referring next to the flow diagram of FIG. 5, there is illustrated thesignalling and communications processes executed by microcomputer 202 inaudio logic control unit 200 in FIG. 2 under control of the firstportion of the control program for cellular system A. Initially, display304 in handset unit 300 is loaded with a pre-selected message indicatingsystem A operation and is subsequently cleared in response to the firstkey activation. The flow diagram of FIG. 5 is entered at block 502 inresponse to either an interrupt, the reset signal or when returning fromsystem B. After initialization, the dedicated control channels arescanned at block 504 and the two strongest control channels areselected. If no service is available in system A for a predeterminedperiod of time, program control may transfer in response to an interruptfrom the first portion of the control program to the second portion ofthe control program for operation in cellular system B, as illustratedin FIG. 7. For example, a no service condition would arise when thecellular telephone moves from a city covered by cellular system A to ahighway or another city covered only by cellular system B. In thissituation, microcomputer 202 branches to the second portion of thecontrol program for resuming operation in cellular system B so thatcellular service is not interrupted, according to a feature of thepresent invention. If a control channel is selected, the paging channelsare then scanned at block 506 and the two strongest paging channels areselected. If service is available, the overhead message traintransmitted on the paging channel is verified at block 508 andthereafter program control proceeds to idle block 510. From idle block510 a call origination may occur at block 512, location registration maytake place at block 516 and an incoming call termination may beprocessed at block 514. From block 512 or block 514, program controlproceeds to blocks 518, 520 and 522 for processing the call originationor call termination, respectively. At block 518, system access andspeech monitoring is performed and if necessary, a handoff is executedat block 522 or if service is lost a hang-up and disconnection clearingfunction is performed at 520. When the telephone call is terminated,program control is transferred back to block 504 to repeat the foregoingprocess.

Referring next to the flow diagram of FIG. 6, there is illustrated theprocess performed by microcomputer 202 of audio/logic control unit 200in FIG. 2 under control of the second portion of the control program forsignalling and communications in cellular system B. Entering in responseto an interrupt, initialization is performed at block 602. During systemB operation, a "ROAM" indicator in handset unit 300 is continuouslyflashed, and display 304 in handset unit 300 is initially loaded with apre-selected message indicating system B operation and is subsequentlycleared in response to the first key activation. Next, at block 604, theP-channel is scanned, RSSI signal 910 is detected, and the location codeis verified. If no service is available in system B for a predeterminedperiod of time, program control may transfer in response to an interruptfrom the second portion of the control program back to the first portionof the control program to resume operation in cellular system A, asillustrated in FIG. 7. At the time of such transfer, the current systemparameters are stored in the EEPROM memory of microcomputer 202 ofaudio/logic control unit 200 to indicate that operation in cellularsystem B was attempted. If the location code indicates a new locationwas entered, location registration is performed at block 606. Otherwise,program control proceeds to idle block 608 to wait for an outgoing callorigination or an incoming call termination. Also, at block 608, RSSIsignal 910 is continuously checked to determine if an acceptable RFsignal is being received. If RSSI signal 910 is less than level L2,program control transfer back to block 604. As long as the RSSI signalhas a magnitude greater than level L3, program control remains at block608. In the preferred embodiment, levels L2 and L3 correspond to RFsignal levels of -96 dBm and -91 dBm, respectively. From idle block 608,an outgoing call origination may occur at block 612 or an incoming calltermination may be processed at block 614. From block 612 or block 614,program control proceeds to blocks 618, 620 and 622 for processing thecall origination, or call termination, respectively. At block 618, RSSIand speech monitoring is performed and if necessary, a handoff isexecuted at block 622 or, if service is lost, a hang-up anddisconnection clearing function is performed at block 620. When thetelephone call is terminated, program control is transferred back toblock 608 to repeat the foregoing process.

Referring next to the flow diagram of FIG. 7, there is illustrated theprocess performed by microcomputer 202 of audio/logic control unit 200in FIG. 2 for processing interrupts and automatically switching betweencellular systems A and B. Three programmable timers, the Z timer, Xtimer, and Y timer, are used to determine when to switch between systemsA and B. The Z timer is used for timing the loss of service in system A.A suitable value for the Z timer is one minute. The X timer is used fortiming the loss of service in system B. A suitable value for the X timeris one-half minute. The Y timer is used for timing the duration ofservice in system B. A suitable value for the Y timer is one minute.During initialization for system A or B, the Z timer or the X and Ytimers are set to their nominal values and thereafter decremented inresponse to the one millisecond interrupt as explained hereinbelow. Inthe preferred embodiment of the dual-system cellular telephone,automatic switching may also be disabled and switching between systems Aand B may be done manually in response to pre-selected key sequencesentered by the user on keypad 306.

Entering the flow diagram of FIG. 7 in response to the one millisecondinterrupt from the control program for cellular system A, the interrupttimer is checked at block 702 to determine if five milliseconds haselapsed. If five milliseconds has elapsed and service is not availablein system A, the Z timer is decremented at block 704. If service isavailable in system A, the Z timer is set to its nominal value again.Next, at block 706, a status check is made to determine if the Z timerhas been decremented to zero. If the Z timer has been decremented tozero, then at block 708, the X and Y timers are set to their nominalvalues and the system A call parameters are saved. Thereafter, operationis switched to system B by branching to the second portion of thecontrol program when returning from the one millisecond interrupt.Entering the flow diagram of FIG. 7 in response to the one millisecondinterrupt from the control program for cellular system B, the interrupttimer is checked at block 702 to determine if five milliseconds haselapsed. If five milliseconds has elapsed and service is not availablein system B, the X timer is decremented at block 704. If service isavailable in system B, the X timer is set to its nominal value again. Iffive milliseconds has elapsed, the Y timer is decremented at block 704.Next, at block 706, a status check is made to determine if the X or Ytimer has been decremented to zero. If the X or Y timer has beendecremented to zero, then at block 710, the Z timer is set to itsnominal value and the system B call parameters are saved. Thereafter,operation is switched to system A by branching to the first portion ofthe control program when returning from the one millisecond interrupt.Even if service is available in System B, the Y timer will decrement tozero and result in switching back to system A, since operation in systemA is preferred. If there is no preferred system, only the Z and X timersare needed in other embodiments.

In summary, a unique dual-system cellular telephone includes bandwidthswitching in the receiver thereof and software switching in the controlunit for automatically operating on different cellular telephonesystems. Bandwidth switching may be accomplished by switching betweendifferent filters in the intermediate frequency section of the receiverof the dual-system cellular telephone depending on which cellulartelephone system is available. Software switching may be accomplished byswitching between different portions of the control program in thecontrol unit of the dual-system cellular telephone depending on whichcellular telephone system is available. When service is not available inone of the cellular telephone systems, the unique dual-system cellulartelephone automatically switches to the other cellular telephone system.

I claim:
 1. A cellular telephone communicating cellular telephone callson at least first and second cellular telephone systems each havingdifferent cellular radio channels, said cellular telephonecomprising:antenna means for receiving and transmitting cellulartelephone call signals on said cellular radio channels; dialing meansfor dialing digits of telephone numbers; cellular transmitting meanscoupled to the antenna means for transmitting cellular telephone callsignals on the cellular radio channels of the first and second cellulartelephone systems; cellular receiving means coupled to the antenna meansfor receiving cellular telephone call signals on the cellular radiochannels of the first and second cellular telephone systems, saidcellular receiving means further including intermediate frequency meanshaving first filtering means having a first predetermined bandwidth,second filtering means having a second predetermined bandwidth that hasa magnitude less than that of the first predetermined bandwidth, andswitching means responsive to a bandwidth control signal having firstand second states for switching between the first and second filteringmeans, respectively; and control means including memory means forstoring first and second control programs, said control means beingcoupled to the dialing means, cellular transmitting means, and cellularreceiving means for automatically transmitting and receiving cellulartelephone calls on the first cellular telephone system using the firstcontrol program and on the second cellular telephone system using thesecond control program, said control means generating the first state ofthe bandwidth control signal for cellular telephone calls on said firstcellular telephone system and generating the second state of thebandwidth control signal for cellular telephone calls on said secondcellular telephone system, and said control means monitoring thecellular radio channels to detect the absence of cellular service andswitching between the first and second cellular telephone systems whencellular service has been absent for a predetermined time interval. 2.The cellular telephone according to claim 1, wherein said first andsecond filtering means include first and second ceramic filter means,respectively.
 3. The cellular telephone according to claim 1, whereinsaid switching means includes analog switch means.
 4. The cellulartelephone according to claim 1, wherein said cellular transmitting meansfurther includes power amplifying means responsive to a PA controlsignal for amplifying the cellular telephone call signals, means fordetecting the magnitude of the amplified cellular telephone callsignals, and means responsive to the detected magnitude of the amplifiedcellular telephone call signals for generating the PA control signal. 5.A cellular telephone communicating cellular telephone calls on at leastfirst and second cellular telephone systems each having differentcellular radio channels, said cellular telephone comprising:antennameans for receiving and transmitting cellular telephone call signals onsaid cellular radio channels; transmitter filtering means coupled to theantenna means for filtering the transmitted cellular telephone callsignals; receiver filtering means coupled to the antenna means forfiltering the received cellular telephone call signals; dialing meansfor dialing digits of telephone numbers; cellular transmitting meanscoupled to the transmitter filtering means for transmitting cellulartelephone call signals on the cellular radio channels of the first andsecond cellular telephone systems; cellular receiving means coupled tothe receiver filtering means for receiving cellular telephone callsignals on the cellular radio channels of the first and second cellulartelephone systems, said cellular receiving means further includingintermediate frequency means having first filtering means having a firstpredetermined bandwidth, second filtering means having a secondpredetermined bandwidth that has a magnitude less than that of the firstpredetermined bandwidth, and switching means responsive to a bandwidthcontrol signal having first and second states for switching between thefirst and second filtering means, respectively; and control meansincluding memory means for storing first and second control programs,said control means being coupled to the dialing means, cellulartransmitting means, and cellular receiving means for automaticallytransmitting and receiving cellular telephone calls on the firstcellular telephone system using the first control program and on thesecond cellular telephone system using the second control program, saidcontrol means generating the first state of the bandwidth control signalfor cellular telephone calls on said first cellular telephone system andgenerating the second state of the bandwidth control signal for cellulartelephone calls on said second cellular telephone system, and saidcontrol means monitoring the cellular radio channels to detect theabsence of cellular service and switching between the first and secondcellular telephone systems when cellular service has been absent for apredetermined time interval.
 6. The cellular telephone according toclaim 5, wherein said first and second filtering means include first andsecond ceramic filter means, respectively.
 7. The cellular telephoneaccording to claim 5, wherein said switching means includes analogswitch means.
 8. The cellular telephone according to claim 5, whereinsaid cellular transmitting means further includes amplifying meansresponsive to a gain control signal for amplifying the cellulartelephone call signals, means for detecting the magnitude of theamplified cellular telephone call signals, and means responsive to thedetected magnitude of the amplified cellular telephone call signals forgenerating the gain control signal.
 9. A cellular telephonecommunicating cellular telephone calls on at least first and secondcellular telephone systems each having different cellular radiochannels, said cellular telephone comprising:antenna means for receivingand transmitting cellular telephone call signals on said cellular radiochannels; dialing means for dialing digits of telephone numbers;cellular transmitting means coupled to the antenna means fortransmitting cellular telephone call signals on the cellular radiochannels of the first and second cellular telephone systems; cellularreceiving means coupled to the antenna means for receiving cellulartelephone call signals on the cellular radio channels of the first andsecond cellular telephone systems, said cellular receiving means furtherincluding:first intermediate frequency means including first filteringmeans having a first predetermined bandwidth for generating a firstintermediate frequency signal; second intermediate frequency meansincluding second filtering means having a second predeterminedbandwidth, third filtering means having a third predetermined bandwidththat has a magnitude less than that of the second predeterminedbandwidth, said second intermediate frequency means coupled to the firstintermediate frequency signal for generating a second intermediatefrequency signal; detecting means coupled to the second intermediatefrequency signal for detecting the received cellular telephone callsignals; and switching means responsive to a bandwidth control signalhaving first and second states for switching between the second andthird filtering means, respectively; and control means including memorymeans for storing first and second control programs, said control meansbeing coupled to the dialing means, cellular transmitting means, andcellular receiving means for automatically transmitting and receivingcellular telephone calls on the first cellular telephone system usingthe first control program and on the second cellular telephone systemusing the second control program, said control means generating thefirst state of the bandwidth control signal for cellular telephone callson said first cellular telephone system and generating the second stateof the bandwidth control signal for cellular telephone calls on saidsecond cellular telephone system, and said control means monitoring thecellular radio channels to detect the absence of cellular service andswitching between the first and second cellular telephone systems whencellular service has been absent for a predetermined time interval. 10.The cellular telephone according to claim 9, wherein said first andsecond filtering means include first and second ceramic filter means,respectively.
 11. The cellular telephone according to claim 9, whereinsaid switching means includes analog switch means.
 12. The cellulartelephone according to claim 9, wherein said cellular transmitting meansfurther includes power amplifying means responsive to a PA controlsignal for amplifying the cellular telephone call signals, means fordetecting the magnitude of the amplified cellular telephone callsignals, and means responsive to the detected magnitude of the amplifiedcellular telephone call signals for generating the PA control signal.13. A cellular telephone communicating cellular telephone calls on afirst set of cellular radio channels having a first cellular telephonesignalling protocol and a second set of cellular radio channels having asecond cellular telephone signalling protocol, said cellular telephonecomprising:antenna means for receiving and transmitting cellulartelephone call signals on said cellular radio channels; dialing meansfor dialing digits of telephone numbers; synthesizing means forgenerating a reference signal; cellular transmitting means coupled tothe antenna means for transmitting cellular telephone call signals onsaid cellular radio channels; cellular receiving means coupled to theantenna means and the reference signal for receiving cellular telephonecall signals on said cellular radio channels, said cellular receivingmeans further including intermediate frequency means havingdual-bandwidth filtering means and switching means for generating anintermediate frequency signal having a predetermined frequency, thedual-bandwidth filtering means switchable between a first predeterminedbandwidth and a second predetermined bandwidth that has a magnitude lessthan that of the first predetermined bandwidth, and the switching meansbeing responsive to a bandwidth control signal having first and secondstates for switching said dual-bandwidth filtering means between thefirst and second predetermined bandwidths, respectively; and controlmeans including memory means for storing first and second controlprograms, said control means being coupled to the dialing means,cellular transmitting means, and cellular receiving means forautomatically transmitting and receiving cellular telephone calls on thefirst set of cellular radio channels using the first control program andon the second set of cellular radio channels using the second controlprogram, said control means generating the first state of the bandwidthcontrol signal for cellular telephone calls on said first set ofcellular radio channels and generating the second state of the bandwidthcontrol signal for cellular telephone calls on said second set ofcellular radio channel.
 14. The cellular telephone according to claim13, wherein said dual-bandwidth filtering means includes first filteringmeans having the first predetermined bandwidth and second filteringmeans having the second predetermined bandwidth.
 15. The cellulartelephone according to claim 13, wherein said switching means includesanalog switch means.
 16. The cellular telephone according to claim 13,wherein said cellular transmitting means further includes poweramplifying means responsive to a PA control signal for amplifying thecellular telephone call signals, means for detecting the magnitude ofthe amplified cellular telephone call signals, and means responsive tothe detected magnitude of the amplified cellular telephone call signalsfor generating the PA control signal.
 17. A cellular telephonecommunicating cellular telephone calls on a first set of cellular radiochannels having a first cellular telephone signalling protocol and asecond set of cellular radio channels having a second cellular telephonesignalling protocol, said cellular telephone comprising:antenna meansfor receiving and transmitting cellular telephone call signals on saidcellular radio channels; transmitter filtering means coupled to theantenna means for filtering the transmitted cellular telephone callsignals; receiver filtering means coupled to the antenna means forfiltering the received cellular telephone call signals; dialing meansfor dialing digits of telephone numbers; synthesizing means forgenerating a reference signal; cellular transmitting means coupled tothe transmitter filtering means for transmitting cellular telephone callsignals on said cellular radio channels; cellular receiving meanscoupled to the receiver filtering means and the reference signal forreceiving cellular telephone call signals on said cellular radiochannels, said cellular receiving means further including intermediatefrequency means having dual-bandwidth filtering means and switchingmeans for generating an intermediate frequency signal having apredetermined frequency, the dual-bandwidth filtering means switchablebetween a first predetermined bandwidth and a second predeterminedbandwidth that has a magnitude less than that of the first predeterminedbandwidth, and the switching means being responsive to a bandwidthcontrol signal having first and second states for switching saiddual-bandwidth filtering means between the first and secondpredetermined bandwidths, respectively; and control means includingmemory means for storing first and second control programs, said controlmeans being coupled to the dialing means, cellular transmitting means,and cellular receiving means for automatically transmitting andreceiving cellular telephone calls on the first set of cellular radiochannels using the first control program and on the second set ofcellular radio channels using the second control program, said controlmeans generating the first state of the bandwidth control signal forcellular telephone calls on said first set of cellular radio channelsand generating the second state of the bandwidth control signal forcellular telephone calls on said second set of cellular radio channel.18. The cellular telephone according to claim 17, wherein saiddual-bandwidth filtering means includes first filtering means having thefirst predetermined bandwidth and second filtering means having thesecond predetermined bandwidth.
 19. The cellular telephone according toclaim 17, wherein said switching means includes analog switch means. 20.The cellular telephone according to claim 17, wherein said cellulartransmitting means further includes amplifying means responsive to again control signal for amplifying the cellular telephone call signals,means for detecting the magnitude of the amplified cellular telephonecall signals, and means responsive to the detected magnitude of theamplified cellular telephone call signals for generating the gaincontrol signal.
 21. A cellular telephone communicating cellulartelephone calls on a first set of cellular radio channels having a firstcellular telephone signalling protocol and a second set of cellularradio channels having a second cellular telephone signalling protocol,said cellular telephone comprising:antenna means for receiving andtransmitting cellular telephone call signals on said cellular radiochannels; dialing means for dialing digits of telephone numbers;synthesizing means for generating a reference signal; cellulartransmitting means coupled to the antenna means for transmittingcellular telephone call signals on said cellular radio channels;cellular receiving means coupled to the antenna means and the referencesignal for receiving cellular telephone call signals on said cellularradio channels, said cellular receiving means further including:firstintermediate frequency means including first filtering means having afirst predetermined bandwidth for generating a first intermediatefrequency signal; second intermediate frequency means coupled to thefirst intermediate frequency signal and including dual-bandwidth secondfiltering means for generating a second intermediate frequency signal,the dual-bandwidth filtering means switchable between a secondpredetermined bandwidth and a third predetermined bandwidth that has amagnitude less than that of the second predetermined bandwidth;detecting means coupled to the second intermediate frequency signal fordetecting the received cellular telephone call signals; and switchingmeans responsive to a bandwidth control signal having first and secondstates for for switching said dual-bandwidth second filtering meansbetween the second and third predetermined bandwidths, respectively; andcontrol means including memory means for storing first and secondcontrol programs, said control means being coupled to the dialing means,cellular transmitting means, and cellular receiving means forautomatically transmitting and receiving cellular telephone calls on thefirst set of cellular radio channels using the first control program andon the second set of cellular radio channels using the second controlprogram, said control means generating the first state of the bandwidthcontrol signal for cellular telephone calls on said first set ofcellular radio channels and generating the second state of the bandwidthcontrol signal for cellular telephone calls on said second set ofcellular radio channel.
 22. The cellular telephone according to claim21, wherein said dual-bandwidth second filtering means includes thirdfiltering means having the second predetermined bandwidth and fourthfiltering means having the third predetermined bandwidth.
 23. Thecellular telephone according to claim 21, wherein said switching meansincludes analog switch means.
 24. The cellular telephone according toclaim 21, wherein said cellular transmitting means further includespower amplifying means responsive to a PA control signal for amplifyingthe cellular telephone call signals, means for detecting the magnitudeof the amplified cellular telephone call signals, and means responsiveto the detected magnitude of the amplified cellular telephone callsignals for generating the PA control signal.